Nature

Coconut (Cocos nucifera) is easily identified by its crown of feather-like fronds and clusters of large fruits carried on the top of long slender stems. It grows up to 65-72 ft in 40 years. (1). The fruit of the coconut palm tree is identified as a drupe and not as nuts. The outer layer is made up of green-yellow leathery exocarp color. Underneath is a fibrous mesocarp, and the seed is covered by a woody endocarp (2). The coconut is a synoicous plant with both male and female flowers on the same plant (1).  The typical amount of coconut pollen produced in a single flower ranges from 0.11 million to 0.22 million grains per anther (3). It is mainly used for staple food, woodwork, handicrafts etc. (1). Various components of coconut, such as oil and milk, are utilized for cooking and frying. They are also used in creating soaps, cosmetics and other dermatology products (4).

Habitat

Coconut palm can be seen along the tropical and subtropical regions and primarily observed along the coasts around the world. Its inherent habitat is coastal areas and sandy soil but can adapt to various types of soil. It is a non-invasive plant. Thus, humans’ use can be considered a significant factor for its spread inland from its natural habitat. It survives under humid and warm conditions and can also endure short-term exposure to low temperatures (1).

Taxonomy

Tissue

A typical coconut pollen grain has a single furrow (monocolpate). It ranges from 65 to 69µm in length and 28 to 30 µm in diameter (3).  

Coconut allergy is an infrequent clinical entity. In the small number of cases that have been reported, most of them are associated with anaphylaxis. Other symptoms observed are urticaria, dermatitis, asthma and rhinorrhea.

Studies have shown that exposure to coconut and its allergens may facilitate the risk of coconut sensitization from a young age even after tolerance to coconut in initial years. This exposure may also lead to an increment in allergic reactions with aging in allergic patients(4, 12).

Anaphylaxis

In Spain’s published literature, around nine allergy cases to coconut with anaphylactic reaction have been reported. Among these, four of them occurred in children. The patients may suffer from allergic reactions such as rhinorrhea, sneezing outbursts, spasmodic coughing, vomiting and breathing difficulty (12).

A boy (age three years) suffered from, oral allergy syndrome, vomiting, sudden abdominal pain and eyelids’ edema after ingesting a small portion of fresh coconut. No other food allergies were present. A skin prick test with coconut showed a strong positive response. Testing with sIgE to coconut was also positive (13). 

Contact Urticaria

A literature published case report on mono-sensitization to coconut in a 64-years-old female patient suffering from hypertension and thyroiditis. The patient developed generalized urticaria, facial and uvula edema, dysphagia and dyspnea. Another episode followed where hypoxemia (low oxygen levels), hypotension (low blood pressure), and bronchoconstriction reactions were observed (14).

Atopic Dermatitis

Coconut fatty acids diethanolamine is a by-product of coconut oil. In a study conducted on a total of 2572 subjects with occupational allergic contact dermatitis, around 1 percent had allergic dermatitis due to coconut products (15).

Allergic conjunctivitis

A case of occupational allergic conjunctivitis due to coconut fiber dust was reported. A 46-year-old male had been working for about ten years in the factory of coconut fibre mattress. He developed conjunctivitis in the last few years, usually appearing 20 to 30 minutes after tufting of coconut fibre mattress. On the application of the coconut fibre test, he developed symptoms of allergic conjunctivitis. The signs were seen up to 24 hours after the test. An increase in eosinophil count was also found in tear fluid from the patient (16).

Asthma

In a study done in India in 975 individuals, about 2% of patients with coconut sensitivity had asthma and allergic rhinitis. A positive result was found in seven out of a total of eight patients in a test of bronchial provocation (17).

Allergenic molecules

Coconut contains allergens such as Coc n 1(7S globulin) Coc n 2 and Coc n 4 (11S globulin) protein. The Coc n 1, 7S globulin is a vicilin-like protein (2, 4). Coc n 4, cocosin globulin is an allergen with a hexamer structure and a molecular weight of about 300 kDa. This unit has 54 kDa subunit with disulfide bond connecting acid and essential chains (10). Coconut allergens are identified with a different molecular weight, such as 35 kDa, 36.5 kDa and 55 kDa (19).

In a study report of a male patient (age 28 years), an anaphylactic reaction occurred due to coconut ice-cream intake. In this patient, protein bands for the molecular weights of 15, 20, 35, 45 and 200 kDa were shown. Also, IgE immunoblot showed strong reactivity to a protein of 78 kDa and weak for bands 15–20, 22 and 30 kDa (20).

 Among these identified allergens, only Coc n 1 has been listed in the WHO/IUIS list (21).

Biomarkers of severity

Coc n 1, a vicilin-like protein, has been recognized as a major allergen (11). 

Cross-reactivity

Cross-reactivity has been found between coconut and tree nuts such as walnuts, hazelnuts and lentils, and this is mainly due to allergens such as 7S and 11S globulins (12). The coconut’s decreased protein at 35 kDa of coconut 11S globulin is thought to be soy glycinin, a legumin type of seed storage protein (19). In a study of two subjects with an allergy to coconut, the clinical reactivity was found due to cross-reactivity of IgE antibodies for Walnut (19). 7S globulin, which has been described as a major allergen in walnut (Jug n 2, Jug r 2) and hazelnut (Cor a 11), is also identified in coconut (10).

Though in general correlation between patients sensitized or allergic to tree-nut or peanuts with sensitization to coconut has not been observed(7, 8). One study in the children population reported high significant coconut co-sensitization rates with 71% for macadamia and 69% for almond. In another case report, two patients, who had a history of anaphylactic reaction to walnut, developed an anaphylactic reaction to coconut, signifying co-sensitization (8).

There also exists cross-reactivity between latex and coconut. In a study done in patients with type I latex allergy, about 21.1% of them had a food allergy. Out of these, about 2% had coconut allergy (22).

A study has discovered strong cross-reactivity between buckwheat and coconut. This cross-reaction may be due to Coc n 2 of molecular weight 29 kDa in coconut and Fag e 3 of 19 kDa in buckwheat, known as vicilin-like allergens (23).